Avometer Model 7 Mk2 inside View

The electronic construction of the AVO Model 7 Mk2 is similar to previous models where the front Bakelite panel also serves as a ridged chassis for mounting the meter movement and components. Whilst the outside components are of easy reach for repair, the range selector switch is deep within the wiring and difficult to gain access.

This meter would have been hand assembled all those years ago, and almost any component is replaceable if you can find the parts. When I bought this meter, it was in a right state and the first thing I did was give it a steam clean. After removing the years of grime, I was able to see the components properly to diagnose the faults that it had. One of the problems with meters this old is that the resistors tend to drift in value, and since I wanted precision, I had to replace two resistors to achieve a satisfactory performance.

This meter has a very large oil condenser, which usually contains Pyranol. This would have been an expensive component to include back then, but vital to the proper operation of the circuit.

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